The present invention relates to various magnetic heads including an induction type magnetic head, a magnetoresistance type magnetic head (MR head), and an MR induction type composite head having an induction head portion and an MR head portion, and their fabrication method.
In recent years, magnetic recording of much higher density than ever before has been put forward. With this, thin film magnetic heads using soft magnetic thin films as magnetic poles, and reproducing MR heads making use of magnetoresistance effect have been under remarkable developments.
An MR head is designed to read external magnetic signals through a resistance change in a reading sensor formed of magnetic material. A characteristic feature of the MR head is that high outputs are achievable even when magnetic recording is performed at high linear densities because outputs are not dependent on its relative speed with respect to a recording medium. To increase resolving power and obtain good-enough properties at high frequencies, the MR head is usually constructed by sandwiching a magneto-resistance film (an MR film) between a pair of magnetic shielding films (a shielded MR head).
For the MR head that is a reproducing head, an MR induction type composite head is used, in which an MR head portion is provided in the form of an integral piece of an induction type head portion for recording purposes.
For magnetic shielding films or magnetic poles in the MR heads or the MR induction type composite heads, it is preferable to use thin films excellent in soft magnetic properties. Fe--Zr--N base soft magnetic thin films set forth in JP-B 7-60767 and JP-A 3-1513, for instance, are available to this end.
MR films are generally of low heat resistance. In particular, multilayer films having giant magnetoresistance (GMR) effect (artificial lattice films composed of a laminate of thin films each having a thickness of about 5 nm) are likely to undergo considerable degradation because mutual dispersion occurs between thin films upon heated. It is thus required that annealing for the purpose of improving the soft magnetic properties of magnetic shielding films or magnetic poles be done at temperatures below 300.degree. C.
JP-B 7-60767 discloses that a soft magnetic thin film having a coercive force of up to 1 Oe is obtained. However, the lowest annealing temperature described therein is 350.degree. C. The publication states that, in order to obtain excellent soft magnetic properties, the relative intensity ratio of Fe (200) peak to Fe (110) peak should be at least 1 as found by X-ray diffractometry; in another parlance, it is essentially required that the thin film be subjected to preferential orientation on the (100) plane. Illustrated in FIG. 5 of the publication is an X-ray diffraction pattern of a soft magnetic thin film annealed at 600.degree. C. As shown, the relative intensity ratio of Fe (200) peak to Fe (110) peak is 3.1. As also shown, there is a distinctive, broad peak for ZrN. Referring to a mechanism by which soft magnetic properties are improved, the publication states that the growth of crystal grains can be limited by the precipitation of fine grains of ceramics such as ZrN at an Fe grain boundary. To achieve the precipitation of fine grains of the ceramics at the Fe grain boundary, annealing at a temperature exceeding 300.degree. C. is essentially needed. In addition, the precipitation of ZrN offers another problem, i.e., a drop of corrosion resistance due to the precipitation of .alpha.-Fe.
JP-A 3-1513 mentioned above discloses a soft magnetic thin film that is present in the form of an amorphous film immediately upon formation. When this amorphous film is annealed at 350.degree. C. or higher, a low coercive force of 1 Oe or lower is obtained. However, as long as 4,800 minutes are needed for crystallization when annealing is carried out at 250.degree. C. In addition, the coercive force obtained at that time is as high as 1.4 Oe. Illustrated in FIG. 11 of the publication is an X-ray diffraction pattern change due to a change in the annealing temperature. As can be seen from FIG. 11, a broad peak for Fe (200) is present when the annealing is carried out at a high temperature of 450.degree. C. or greater. However, such an Fe (200) peak is not substantially observed when the annealing is performed in a region of temperature that is lower than 450.degree. C. Also, the publication states that if the annealing temperature is at least 350.degree. C., a coercive force of 10 Oe or lower is obtained while a diffraction peak for ZrN is observed. In other words, it is believed that in order that the soft magnetic thin film set forth in the publication has good-enough soft magnetic properties, the presence of ZrN is required as in the case of the soft magnetic thin film disclosed in JP-B 7-60767.
For both soft magnetic thin films set forth in JP-B 7-60767 and JP-A 3-1513 annealings at a temperature of 350.degree. C. or higher are essentially required; in other words, they cannot be applied to magnetic shielding films, and magnetic poles in magnetic heads having MR films of low heat resistance. Thus, it is desired to develop a soft magnetic thin film which, even upon annealed at a temperature below 300.degree. C., can have excellent soft magnetic properties.
JP-A 6-259729, too, describes a soft magnetic thin film having an Fe--Zr--N base composition. As described, this thin film is applied to a magnetic shielding film in MR heads or an MR induction type of composite heads. However, the publication does not show the application of the thin film to a magnetic pole in induction head portions. Moreover, while the publication provides no illustration of an X-ray diffraction pattern of the soft magnetic thin film, it states that the soft magnetic thin film should be subjected to preferential orientation on the (100) plane. The publication goes on that the soft magnetic thin film has an increased thermal stability because the growth of Fe crystal grains is limited by the formation of ZrN. In this soft magnetic thin film, too, ZrN is formed as is the case with JP-B 7-60767 and JP-A 3-1513.
However, JP-A 6-259729 says nothing about whether or not the soft magnetic thin film has been annealed. If any annealing is dispensed with, the soft magnetic thin film will be suitable for MR heads or an MR induction type of composite heads. However, experiments performed by the inventors indicate that it is very difficult to obtain thin films oriented on the (100) plane unless annealing is performed, and so most of them will be oriented on the (110) plane due to slight variations in film-forming conditions such as a partial pressure of nitrogen, power input, and the degree of vacuum at a reactive sputtering step. In the absence of annealing, it is impossible to form ZrN in a stable manner.
An object of the present invention is to prevent any degradation of MR films due to annealings of magnetic shielding films or magnetic poles in MR heads or an MR induction type of composite heads comprising a reproducing MR head portion and a recording induction head portion.